Fatal error: Uncaught TypeError: WP_Translation_Controller::set_locale(): Argument #1 ($locale) must be of type string, null given, called in /var/www/project/web/wp/wp-includes/l10n.php on line 803 and defined in /var/www/project/web/wp/wp-includes/l10n/class-wp-translation-controller.php:87
Stack trace:
#0 /var/www/project/web/wp/wp-includes/l10n.php(803): WP_Translation_Controller->set_locale(NULL)
#1 /var/www/project/web/app/plugins/polylang-pro/vendor/wpsyntex/polylang/include/olt-manager.php(106): load_textdomain('meta-box', '/var/www/projec...')
#2 /var/www/project/web/wp/wp-includes/class-wp-hook.php(326): PLL_OLT_Manager->load_textdomains('fi')
#3 /var/www/project/web/wp/wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters(NULL, Array)
#4 /var/www/project/web/wp/wp-includes/plugin.php(517): WP_Hook->do_action(Array)
#5 /var/www/project/web/app/plugins/polylang-pro/vendor/wpsyntex/polylang/frontend/choose-lang.php(112): do_action('pll_language_de...', 'fi', Object(PLL_Language))
#6 /var/www/project/web/app/plugins/polylang-pro/vendor/wpsyntex/polylang/frontend/choose-lang-url.php(82): PLL_Choose_Lang->set_language(Object(PLL_Language))
#7 /var/www/project/web/app/plugins/polylang-pro/vendor/wpsyntex/polylang/frontend/choose-lang-url.php(34): PLL_Choose_Lang_Url->set_language_from_url()
#8 /var/www/project/web/app/plugins/polylang-pro/vendor/wpsyntex/polylang/frontend/frontend.php(118): PLL_Choose_Lang_Url->init()
#9 /var/www/project/web/app/plugins/polylang-pro/vendor/wpsyntex/polylang/include/class-polylang.php(285): PLL_Frontend->init()
#10 /var/www/project/web/app/plugins/polylang-pro/vendor/wpsyntex/polylang/include/class-polylang.php(228): Polylang->init_context('PLL_Frontend', Object(PLL_Model))
#11 /var/www/project/web/wp/wp-includes/class-wp-hook.php(324): Polylang->init('')
#12 /var/www/project/web/wp/wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters(NULL, Array)
#13 /var/www/project/web/wp/wp-includes/plugin.php(517): WP_Hook->do_action(Array)
#14 /var/www/project/web/wp/wp-settings.php(555): do_action('plugins_loaded')
#15 /var/www/project/web/wp-config.php(15): require_once('/var/www/projec...')
#16 /var/www/project/web/wp/wp-load.php(55): require_once('/var/www/projec...')
#17 /var/www/project/web/wp/wp-blog-header.php(13): require_once('/var/www/projec...')
#18 /var/www/project/web/index.php(10): require('/var/www/projec...')
#19 {main}
  thrown in /var/www/project/web/wp/wp-includes/l10n/class-wp-translation-controller.php on line 87

Fatal error: Uncaught TypeError: WP_Translation_Controller::set_locale(): Argument #1 ($locale) must be of type string, null given, called in /var/www/project/web/wp/wp-includes/l10n.php on line 803 and defined in /var/www/project/web/wp/wp-includes/l10n/class-wp-translation-controller.php:87
Stack trace:
#0 /var/www/project/web/wp/wp-includes/l10n.php(803): WP_Translation_Controller->set_locale(NULL)
#1 /var/www/project/web/wp/wp-includes/l10n.php(959): load_textdomain('default', '/var/www/projec...', NULL)
#2 /var/www/project/web/wp/wp-includes/class-wp-fatal-error-handler.php(49): load_default_textdomain()
#3 [internal function]: WP_Fatal_Error_Handler->handle()
#4 {main}
  thrown in /var/www/project/web/wp/wp-includes/l10n/class-wp-translation-controller.php on line 87